1. Field of the Invention
The present invention relates generally to a method and system for scaling a display size between different types of user agents, and more particularly, to a method and system for scaling a display size between different types of user agents, in which, when data are sent between two different user agents performing video communication through a network, the display size of each of the user agents is scaled by using media information that is included in and exchanged between the user agents.
2. Description of the Related Art
VoIP (Voice over Internet Protocol), a service delivering video, audio, and facsimile messages over the Internet, sends real-time media such as audio and video in various situations, such as when a user accesses the Internet via a personal computer (PC), using an independent device to which IP (Internet Protocol) is applied, or by making a telephone call by means of a gateway at a public switched telephone network (PSTN) station.
The VoIP requires a means for finding and signaling a counterpart intended for communication when providing service. There are two kinds of this VoIP signaling: H.323 of Telecommunication Standardization Sector of the International Telecommunications Union (ITU-T), and SIP (Session Initiation Protocol) of Internet Engineering Task Force (IETF).
For some time, VoIP services have been developed based on the H.323. However, the SIP, which is currently on the rise, has easy parsing and compiling, excellent extensibility, and also has the advantage over the H.323 of being easily implemented because it is based on text.
The SIP is used as an application layer control protocol for generation, modification, and termination of a multimedia session or call between at least two user agents in an IP-based network, and includes multimedia conference, internet telephone call, remote education, and other functions. The SIP is modeled on the basis of SMTP (Simple Mail Transfer Protocol), E-mail, HTTP (Hypertext Transfer Protocol), and Web.
As such, the SIP may be referred to as a client-server protocol where a client sends a request and where a server receives the request and sends a response.
The SIP controls the architecture of an incorporated protocol, such as RSVP (Resource Reservation Protocol) for reservation of network resources, RTP (Real-Time Protocol) for real-time data transmission and provision of QoS (Quality of Service) feedback, RTSP (Real Time Streaming Protocol) for transmission control of streaming media, SAP (Session Announcement Protocol) for advertising a multimedia session through a multicast, and SDP (Session Description Protocol) for description of a multimedia session. However, the SIP functions and operates independent of any one of these protocols.
An SIP address is allocated to a user of each host in the format of an E-mail address, such as user@host. For example, as in test@sam.com, kim@sam.com, or 010-9000-10000@165.213.238.1, a part designating the user maybe a name, a telephone number, etc., of the user, and a part designating the host may be a domain name or an IP address. Thus, in most cases, a user's SIP URL (Uniform Resource Locator, previously Universal Resource Locator) can be inferred from the user's E-mail address.
The user client makes use of an SIP server address of a receiver when sending an SIP request. Here, when the SIP server address is a numerical IP address, the user client sends the SIP request to the corresponding IP address. In contrast, when the SIP server address is made up of the domain name, the user client locates the IP address with reference to a DNS (Domain Name Server), and then sends the SIP request. When receiving the SIP request, the SIP server of the receiver makes it possible to gain access to a location server, check location information registered by a registration procedure of the receiver, and then send the SIP request to the receiver.
A flow of messages for call connection between a UAC (User Agent Client) and a UAS (User Agent Server), according to conventional art, is problematic, wherein the media information includes a type of the media (video, audio, etc.), a transfer protocol (RTP/UDP/IP, H.320, etc.), a format of the media (H.261 video, MPEG video, etc.), and so forth.
Since the exchanged media information includes only information on the type, compression method, etc., of the media, the determination of whether the media is processible, and consequently whether to send an acknowledgement message to establish a call, is based solely on such information.
In this scheme, it is a display size of each user agent that is problematic. In the case of exchanging only information on the compression method, information on the display size is not included, video data are encoded and sent at the display size of the sending side. If the display size of the sending side is not equal to that of the receiving side, phenomena such as afterimage, cropping, breakdown, and so forth, occur while data received on the receiving side are decoded and output on a screen.